The present disclosure relates to the manufacturing of solar cells, and in particular to a method that can be used to determine the cleanness of a semiconductor substrate as well as the number of pin holes that may exist within a patterned antireflective coating (ARC) that is present on a front side surface of the substrate. The present invention also provides a solar cell including a patterned antireflective coating located on a front side surface of a semiconductor substrate in which the patterned antireflective coating includes metallic filled pin holes therein.
Photovoltaic solar cells, i.e., devices which convert photons from sunlight into electricity, are regarded as one of the key technologies which will lead to a sustainable energy future. In order for solar energy to be cost competitive and comparable with non-renewable sources of energy (such as, for example, oil, coal and natural gas), low cost processing and high efficiency solar cells are essential.
The majority (over 90%) of solar cells currently in production are based on silicon wafers with screen printed metal pastes as electrical contacts. Screen printing is attractive due to its simplicity in processing and high throughput capability; however, the high contact resistance, high paste cost, shadowing from wide conductive lines, high temperature processing, and mechanical yield loss are disadvantages that have not been overcome even after thirty plus years of research and development.
In a typical screen printing process used in forming a metallic grid on a front side surface of a semiconductor substrate, a thin layer of silicon nitride is used as an antireflective coating (ARC) prior to screen printing the metallic grid. The silicon nitride layer improves the adsorption of sunlight into the semiconductor substrate through the front side surface which will be converted to electricity. The silicon nitride layer is usually deposited on a textured surface, which is very rough with surface topography of micron size tall features. During the formation of the silicon nitride layer, pin holes are introduced into the silicon nitride film. The presence of pin holes provides the silicon nitride layer with a porosity. It has been impossible to characterize the porosity of such silicon nitride films. The porosity of the silicon nitride film caused by these pin holes tends to adversely impact the film's optical properties and silicon surface passivation properties, which adversely impact the final solar cell performance.